Chemical composition of atmospheric aerosols in the general environment and around a trunk road in the Tokyo metropolitan area

To evaluate the influence of vehicle exhaust particles on the urban atmosphere, atmospheric aerosols collected in the general environment and at a trunk road sampling site in the Tokyo metropolitan area were analyzed for carbonaceous and ionic components. Samples were collected as fine (<2.1 μm) and coarse particle (2.1–7.0 μm) from April 2003 to March 2004 using low-volume Andersen sampler. The carbonaceous components were analyzed by a thermal method and a thermal/optical method. Elemental carbon (EC) determined by thermal method was higher than those by thermal/optical method, and slope of linear regression of the thermal method versus the thermal/optical method differed at both sampling points. These results suggested possible analytical artifacts, a difference in the composition of the carbonaceous components of the aerosols, or both. The EC concentrations in fine particles in the roadside were higher than in the general environment by 5 μg m−3, and it was accounted for 68% of the difference of the mass concentration. The mass concentration reconstructed by the mass closure model using element analysis results corresponded more closely to the observed mass concentration in the general environment samples than in the roadside samples. It is suggested that the contribution of the organic compounds in the roadside particles was underestimated. Diesel vehicle emission control regulations implemented in October 2003 seem to have had an effect because there was a significant difference in the average concentration of suspended particulate matter and NOx before and after implementation of the regulations. Moreover, the EC/TC ratio has been decreasing over time.